Reforming processes are conventionally effected in tubular reformers, with catalyst packed into a plurality of reactor tubes. Heat is applied directly to and transferred through the walls of the tubes in a manner to maintain radial and axial temperature profiles inside the tubes within required limits, and this approach has been more-or-less successful. However, it does require the establishment of a fine balance between reaction and heat transfer within the tubes, heat transfer to the outside of the tubes and pressure drop.
The establishment of this balance and the consequential need for relatively large catalyst particles result in low catalyst effectiveness and the need for reformers that are inherently bulky. The catalyst effectiveness might be enhanced and the size of the reformers might be reduced if smaller catalyst particles having higher activity were to be used, but pressure-drop constraints would then dictate the use of many, parallel, short tubes in the reformers.
Some consideration has been given to the possible development of an alternative to the tubular reformers; that is, to the use of so-called printed circuit heat exchanger (“PCHE”) cores and to the deposition of thin layers of reforming catalyst into channels of plates that form the cores. The PCHE cores currently are used in heat exchangers, and they are constructed by etching channels having required forms and profiles into one surface of individual plates which are then stacked and diffusion bonded to form cores having dimensions required for specific applications.
However, whilst this alternative (projected) approach does indicate some merit, several problems are foreseen, including the following:    Difficulties in obtaining adhesion of catalyst to the metal (plate) substrate,    Limited catalyst life,    Difficulties in replacing the catalyst, and    Coupling of heat transfer and catalyst areas, this requiring very high-activity catalyst if over-investment in heat exchange surface is to be avoided.
A partial solution to these problems is revealed in United States Patent Publication US2002/0018739 A1, dated 14 Feb. 2002, which (without constituting common general knowledge) discloses a chemical reactor having a PCHE-type core. The core is constructed with alternating heat exchange and catalyst-containing zones that together form a passageway for a reactant. Each of the heat exchange zones is formed from stacked diffusion bonded plates, with some of the plates providing channels for (externally heated or cooled) heat exchange fluid and others of the plates providing orthogonally directed channels to carry the reactant from one catalyst-containing zone to the next such zone.
The present invention in one of its applications is directed to a development which alleviates at least some of the problems of tubular reformers and which facilitates or extends, in a novel way, the use of PCHE cores in chemical reactors.